Conventionally, Joint Detection (hereinafter referred to as “JD”) demodulation is used as a demodulation method in CDMA mobile communications. JD demodulation is a demodulation method that uses an interference cancellation equalization method that obtains a signal free of inter-code interference or effects of interference on other users. Specifically, a demodulated signal is obtained by performing computation that cancels inter-code interference and effects of interference on other users from a received signal by using a delay profile obtained by means of channel estimation and spreading codes for all users.
FIG. 24 is a block diagram showing the schematic configuration of a conventional JD demodulation apparatus. A conventional JD demodulation apparatus is composed of a channel estimation section 50 and a JD demodulation section 51. The JD demodulation section 51 is composed of a cross-correlation matrix generation section 52 and an interference cancellation computation section 53.
The channel estimation section 50 performs channel estimation processing using a known signal sequence included in a received baseband signal, and generates a delay profile for all multiplex codes of all multiplex users. The cross-correlation matrix generation section 52 of the JD demodulation section 51 generates a cross-correlation matrix based on a delay profile generated by the channel estimation section 50 and spreading code information for all multiplex codes of all multiplexed users. Using the cross-correlation matrix generated by the cross-correlation matrix generation section 52 and the received baseband signal, the interference cancellation computation section 53 performs computation that cancels inter-code interference and effects of interference on other users. The above spreading code information can be obtained from a separately provided spreading code estimation section (not shown) or from a higher layer.
Information concerning conventional JD demodulation is given in, for example, “Interference Cancellation vs. Channel Equalization and Joint Detection for the Downlink of C/TDMA Mobile Radio Concepts” (Bernd Steiner, Proceedings of EPMCC Conference Germany 1997, No.145, pp.253–260) or “EFFICIENT MULTI-RATE MULTI-USER DETECTION FOR THE ASYNCHRONOUS WCDMA UPLINK” (H. R. Karimi, VTC'99, pp.593–597).
However, with a demodulation apparatus using conventional JD demodulation, while the performance of JD demodulation is good compared with normal RAKE demodulation, there are problems in that the amount of computation is large, and power consumption is high.